Many of today's electronic goods contain one or more electronic components that operate at elevated temperature requiring some type of thermal management system. By way of example, desktop or portable computers have one or more microelectronic packages that generate a considerable amount of thermal energy dissipated as heat. An example of a microelectronic package is an integrated circuit microprocessor, an example of which is a central processing unit (CPU) for the computer system.
In many cases, the heat can be managed with the attachment of a thermal conducting device having a large surface area to dissipate the heat into the environment. Such devices are known as heat sinks. Heat sinks are generally formed from a material having a high thermal conductivity comprising a broad base for coupling with the top of the microelectronic package and a series of fins or pins through which air may pass to dissipate the heat. In many cases, a fan is attached to the heat sink to provide forced convection for more efficient heat dissipation.
The attachment of a relatively massive heat sink, and possibly a heavy fan as well, to a microelectronic package involves a number of challenges. The microelectronic package is commonly coupled to a system substrate through an attachment structure, such as a pin grid array socket. A thermal conductive interface material, such as a soft foil, is placed between the top of the microelectronic package and the base of the heat sink to provide intimate thermal contact between the two. Plastic springs and metal side spring clips are some of the common devices used to hold the heat sink to the microelectronic package.
Computer systems are subjected to mechanical shock due to handling. A mechanical shock or impact to the computer system in a direction normal to the top of the microelectronic package, referred to as the “z” direction, can cause the heat sink to lift off of the top of the microelectronic package to be forced back into contact by the spring clamps. It is not uncommon that currently used attachment devices permit the heat sink to lift off of the microelectronic package by as much as 0.06 inch in response to an upward impact of 50 G acceleration used in testing such devices. This movement is not only a source of potential damage to the microelectronic package from the high dynamic forces due to the back-slap of the heat sink, the heat sink can become dislodged or thermally separated from the thermal interface material, drastically degrading thermal performance.
The heat sink attachment must also be able to compensate for different manufacturing tolerance accumulation from part to part. Contributors to tolerance issues include, but are not limited to, chassis standoff, system board, retention mechanism, socket, interposer, microelectronic package, thermal interface material, heat sink, solder reflow, and bolt length.
Further, some types of thermal interface materials experience a change in thickness over time. This dimensional change must be compensated for to ensure continuous intimate contact between the microelectronic package and the heat sink.
Improved heat sink attachment devices and methods are needed to prevent damage due to mechanical shock, to accommodate for manufacturing tolerances, as well as to accommodate for changes in dimensions over time. The attachment device should have the capability to be used for a number of heat sink/microelectronic package configurations to reduce inventory burdens and simplify assembly.